1. Field of the Invention
This invention relates to improved methods and materials for providing adhesive bonding of acrylic resins to industrial, natural, and dental substrates, and more particularly to dental restoration methods and methods of improving adhesion of dental composite restoratives to dentin. More specifically, methods and materials for strong adhesive bonding of composite resins to dentin are disclosed with the objects of improving the treatment of cervical erosions, root caries, and other dental conditions, eliminating much of the mechanical cutting of dentin and enamel currently required for mechanical retention of restorations.
2. Description of the Prior Art
For many years, advances in the study of methods of adhesive bonding of composite materials to hard tooth tissues have evolved in small increments. Swiss Patent No. 687,299 to deTrey, Inc. described a material for bonding to dentin. A more recent patent, U.S. Pat. No. 4,540,722 to 3M Company describes a modification of the original deTrey material. U.S. Pat. Nos. 4,514,527; 4,521,550; 4,588,756; and 4,659,751 all to R. L. Bowen, assigned to the American Dental Association Health Foundation, disclose more recent developments based on the use of mordants and adhesion promoting coupling agents. Each of these steps has resulted in incremental improvements in bonding to dentin, to the point where it is presently feasible for the dentist to use adhesive bonding to retain composite restorations.
The prior art closest to the present invention is the Bowen U.S. Pat. No. 4,659,751, which preferably employed a two-step technique. This technique comprised, first, treating the surface to be bonded with an acidic solution preferably containing nitric or other strong acid, polyvalent cations, and compounds such as oxalic acid or other polyfunctional acids which can form relatively water-insoluble precipitates with calcium and other polyvalent cations at pH values above that of the acidic aqueous treatment solution, and also containing at least one compound selected from the group consisting of (1) N-phenylglycine ("NPG"), (2) the adduct of N(p-tolyl)glycine and glycidyl methacrylate ("NTG-GMA"), (3) the addition reaction product of N-phenylglycine and glycidyl methacrylate ("NPG-GMA"), and (4) other amino acids. Second, the technique called for applying a solution containing at least one monomeric compound selected from the group consisting of (1) the addition reaction product of pyromellitic acid dianhydride and 2-hydroxyethyl methacrylate ("PMDM"), (2) the addition reaction product of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 2-hydroxyethyl methacrylate ("BTDA-HEMA"), and (3) 4-methacryloxyethyltrimellitic anhydride ("4-META").
Alternatively, but less preferred, in the case of vital dentin, according to the Bowen U.S. Pat. No. 4,659,751, the surface to be treated could be contacted with a strongly acidic solution, but still containing NPG, NTG-GMA, NPG-GMA, and/or other amino acids, followed by contacting with PMDM, BTDA-HEMA and/or 4-META monomer solution. Also, an acidic solution and the NPG or other amino acid solution could be applied separately, one after the other (instead of as a combined solution) before the PMDM or other monomer is applied. The components for practicing the method of this Bowen invention are said to be conveniently made available in the form of a kit or article of manufacture described in that patent.
A particularly preferred method of the Bowen invention of U.S. Pat. No. 4,659,751 is accomplished by treating the surface of the dentin, enamel or other substrate containing or capable of binding metallic ions with a solution with contains (1) at least one salt of a polyvalent cation which can bind to substrate surface sites; (2) a compound which contains at least one acid group and preferably two or more acidic groups (3) a strong acid; and (4) at least one surface-active compound selected from the group consisting of NPG, alpha or beta amino acids, and other compounds, each of which contain at least one of each of the following groups: carboxyl and amino. The surface-active compound may be a surface-active comonomer which contains a moiety capable of free radical polymerization as well as the carboxyl and amino groups. The resultant substrate surface is then treated with a solution which contains at least one compound selected from the group consisting of (1) PMDM, (2) BTDA-HEMA, (3) 4-META, (4) other compounds containing at least one group or moiety capable of free radical polymerization, and at least one aromatic ring or moiety containing, electron-withdrawing substituents which do not interfere with free radical polymerization, and which compound preferably also contains one or more free carboxyl groups, or anhydride groups which can form free carboxyl groups upon hydrolysis, and (5) camphoroquinone.